A sleeve fits over the distributor cam, which has cobalt magnets inside it that are detected by the electronic unit, allowing detection of the cam's rotation without physical contact and wear. Everything fits inside the distributor body, meaning that the stock appearance is maintained.

Having read many approving accounts of this device on various old carmailing lists, I bought one recently and fitted it to my 1967 Ford Thunderbird today. It took maybe half an hour and needed only a screwdriver and pliers. Most of the work was just getting to the distributor, since I needed to remove the air cleaner and a hose for the Thermactor emissions system. It worked perfectly first time, no adjustments needed. Even at idle, the engine ran more smoothly, and the effects are most noticeable at lower speeds -- the engine seems much more sure and steady.

The manufacturer claims that voltage to the spark plugs is more than doubled, making for more reliable and hotter sparks. My experience with a day's running says there are definitely noticeable improvements. Even without that, having no points to burn out nor cam wear is quite an improvement - no deterioration with wear.